The present invention generally relates to an induction heating apparatus and more particularly, to an improved exciting arrangement for an induction heating apparatus.
Conventionally, in the induction heating apparatuses generally employed, for example, for cooking purposes and the like, it has been so arranged that, as shown in FIG. 1, an induction heating coil M is disposed adjacent to and below the under surface of a top or upper plate P1 which is made of ceramic material or the like, and on which a vessel or container V made of magnetizable material is placed, so that, by causing high frequency current to flow through said heating coil M, alternating magnetic lines of flux are produced from the heating coil M for induction heating of the vessel V and an object to be heated (not shown) accommodated therein.
In the above case, if a bottom plate P2 made of iron or the like is sufficiently spaced from the heating coil M, no particular problems will be invited but, should the bottom plate P2 be disposed close to the lower portion of the heating coil M, the alternating magnetic lines of flux penetrate or pass through the bottom plate P2 as shown by dotted lines in FIG. 1, and thus, the vessel V and the bottom plate P2 are undesirably heated simultaneously, both acting as loads, with consequent reduction of heating efficiency with respect to the vessel V. Furthermore, upon heating of the bottom plate P2, electronic parts, etc. (not shown) mounted on said bottom plate P2 are adversely affected, while the alternating magnetic lines of flux generated by the heating coil M also exert unfavorable influence on electronic circuits (not shown) incorporated in the heating apparatus, thus resulting in malfunctions thereof.
Therefore, the distance between the top plate P1 and the bottom plate P2 is consequent limited, and thus, from the fact that the height of the heating apparatus can not be made excessively low, efficient operation of the apparatus, for example, during cooking has been undesirably impaired.
In order to eliminate the disadvantage as described above, there has conventionally been proposed an arrangement in which a bar member of ferrite material is attached to the lower portion of the heating coil, but no appreciable effect has been achieved thereby.
In another prior art disclosed, for example, in U.S. Pat. No. 3,710,062 patented Jan. 9, 1973, it is so arranged that a metallic support plate of aluminum is provided below a heating coil or alternatively the heating coil is acommodated in a ferrite core member. However, even by the known arrangement as described above, the disadvantages as stated earlier are not fully eliminated, still presenting some inconvenience in the actual applications.